It is well known to prepare films by implanting ions into a substrate. The implanted ions change the physical and/or electronic properties of the substrate. For example, implanting ions of an electron acceptor, such as boron (B), or an electron donor, such as phosphorous (P), into a silicon (Si) substrate can be used to modify the conductivity of selected regions of the substrate, thus enabling the fabrication of electronic structures such as transistors. It is also known to prepare buried films of silicon dioxide (SiO2) by implanting oxygen (O) ions into an Si substrate. The substrate is subsequently annealed, during which covalent bonds form between the implanted O and the Si substrate to provide SiO2. Buried films of SiO2 prepared by ion implantation have been used, for example, as “barrier layers” that prevent electrical conduction between layers above and below the SiO2.
It is further known to prepare buried films of metal silicide by implanting metal ions into an Si substrate using techniques described in U.S. Pat. Nos. 7,419,915 and 7,419,917 to Abraham, the entire contents of both of which are incorporated by reference herein.
Although films thus formed may in some circumstances be sufficient for conventional applications, the films may suffer from defects. For example, a film intended to be continuous may not actually be continuous, but instead may include large numbers of inclusions and clusters. Or, even if a film is continuous, the interface between the film and the substrate may not be smooth, but instead may include nodule growths. Additionally, it may be difficult, or impossible, to control the phase of the film, potentially resulting in suboptimal performance for a particular application. For example, different phases of a particular material may have drastically different physical, electrical, and/or thermal properties from one another.
Other failings of conventional processing include a limited choice of materials and a restricted range of potential changes to the substrate.